1. Field of the Invention
The present invention relates to a camera, and particularly, to a method and apparatus in which an exposure is automatically adjusted for improving an image quality for a camera phone.
2. Description of the Related Art
Mobile communication systems using mobile communication terminals provide multimedia communication services capable of sending and receiving images as well as audio signals or text messages. According to recent trends in the mobile communication market, mobile communication terminals with built-in cameras have been developed that allow a mobile communication terminal to be used for the multimedia communication and are being used by many mobile communication service subscribers.
A mobile communication terminal with built-in camera (hereinafter, referred to as a camera phone) is a mobile communication terminal having a small digital camera either built-in or attachable thereto. A camera phone allows an object to be photographed, with the photographed image stored in a memory embedded in the mobile communication terminal and further allows the photographic image to be sent to another user with whom a call is established.
In order to photograph an object with good image quality using a camera phone, it is important that illumination of the object is adequate. When the illumination of the object is not adequate, the digital photographic image may contain a noise, which results in degradation of the brightness and color sense of the image. When photographing an object under low illumination, degradation of the image quality may be more pronounced. Therefore, the ability to adjust an exposure appropriate to the corresponding illumination condition is required.
In order to ensure the appropriate illumination of an object, conventional camera phones have a separate optical sensor for measuring the quantity of light from the object in order to determine the illumination of the object. Manual adjustment of the exposure as a dark mode, or a night shot mode, which is an exposure appropriate for photographing an object at low illumination, is provided.
FIG. 1 is a flow chart illustrating a method for photographing an object under low illumination using a conventional camera phone. The method includes a manual adjustment of the illumination mode.
Referring to FIG. 1, a user first previews an object at the current exposure with the camera phone (S10) and determines whether to take a photograph based on the previewed image (S20). If the user determines that the previewed image is adequately illuminated, the object may be photographed (S70).
When photographing an object under low illumination, the user may manually adjust an exposure as a dark mode (S30). If the exposure is not manually adjusted, the user measures the quantity of light of the object using an optical sensor and checks the corresponding illumination level of the previewed image (S40).
If the previewed image is determined to have an illumination lower than a certain level (S50), the user manually adjusts the exposure as a dark mode, or a night shot mode, to increase the exposure time (S60). The manual adjustment is performed using an input/output unit of the camera phone.
The user previews the object in the exposure (S50) and photographs the object (S70) using the exposure (dark exposure mode) as adjusted in the step S60.
However, increasing the exposure time in step S60 causes the object to be photographed by the mobile terminal at a decreased number of frames per second. For example, if a previewed image corresponds to photographing at 30-frames per second and the 30 FPS setting is changed to 15 FPS (for photographing at 15 frames per second) because the illumination value checked by measuring the quantity of light is determined as low illumination, the exposure time is doubled (lengthened). As a result, an image with good quality can be photographed because the exposure time setting with respect to the illumination of the object has an adequate value.
The conventional method for improving an image quality of a camera phone is problematic in that the user must manually adjust the exposure and a separate sensor for measuring the quantity of light of the object is required. In addition, when the object moves, it is difficult to capture and photograph an instantaneous movement by manually adjusting the exposure.
Therefore, there is a need for a camera phone that facilitates automatic adjustment of the exposure used to photograph an object. The present invention addresses these and other needs.